Thanks to everyone who responded. I will say I have gotten a lot more information off this site than from New Holland.
This is where we stand: I would like to change the Ags to Turf tires on my TC29D but there seems to be a big difference in the rim sizes which would result is a big difference in rolling circumference, were I to order the rims recommended in the owner's manual.
The dealer from whom I purchased the tractor referred me to a "tire man" whom he felt would give me a much better deal than I might get purchasing them new from NH (about $2300 for rims and tires). That was genuinely nice and honest of him. This gent seemed to question whether the rim size I gave him from the manual could be accurate, as the diameter would be much less. He recommended I contact the OEM, Titan, and verify the rim specs. I did not follow up with that due to an excessively long telephone que.
Upon recontacting NH, I was disappointed that they would provide no information and no technical advice. They conceded that district managers are trained to tackle technical issues such as this, but would not give out any names. I recontacted my dealer who gave me the name of the District Manager. I emailed him with the quiry regarding the rim diameters and he emailed me back rather promptly and informed me he does not deal on a retail level and provides support for the dealers only. That sucks.
I can only conclude that there is no interest on their (NH's) part in providing any technical information of benefit to the consumer. I consider this to be a significant failure on this company's part and am disappointed that nowhere in there infrastructure can you get an answer to a simple queston. While I will concede this (TC29D) is a mere toy compared to the behemoth tractors that grace their sales lots, my expectations were higher. For now I guess I will just blow it off.